Oil supply system

ABSTRACT

An oil supply system for an internal combustion engine, comprising a lubricating oil circuit in which a first oil pressure generating device, a first device for oil temperature control, and a second device for oil temperature control are provided, wherein the two devices for oil temperature control are arranged in two arms of the lubricating oil circuit connected in parallel and wherein the first oil pressure generating device is arranged in the flow direction upstream of the branch to the two arms leading to the two devices for oil temperature control.

The invention relates to an oil supply system for an internal combustionengine, comprising an oil circuit in which an oil pressure generatingdevice and a device for oil temperature control are provided. Inaddition, the invention relates to an internal combustion enginecomprising such an oil supply system. Finally, the invention relates toa cogeneration plant comprising an internal combustion engine.

BACKGROUND OF THE INVENTION

Internal combustion engines with reciprocating pistons comprise alubricating oil circuit, wherein the engine oil, on the one hand,ensures the lubrication of the bearing points and of the piston assemblyand, on the other hand, protects the surfaces exposed to the blow-bygases from corrosion, and finally cools the pistons. In modernhigh-performance engines, optimum oil supply is essential, as thecomponent load reaches the limit of what is possible and minordisturbances in the lubricating oil circuit can already cause greatdamage.

The optimal temperature range for the engine oil in the internalcombustion engine is between 70 and 95° C. At lower temperatures, therisk of condensate accumulation and acidification of the engine oilarises, at higher temperatures, thermal degradation and, respectively,thermal ageing increase progressively. Furthermore, the viscosity of theengine oil is highly dependent on the temperature, which, in turn, has asubstantial influence on the thickness of the lubricating film. Thetemperature of the engine oil is, in turn, coupled to the cooling watertemperature, since the engine oil is generally cooled by the enginecooling water, or the engine cooling water and the engine oil areincorporated into the same external cooling circuit (e.g., heating watersystem of the internal combustion engine system in cogeneration plants).

In addition to bearing lubrication and bearing cooling, the engine oilalso serves for cooling the pistons. For this purpose, the engine oil isinjected for example through nozzles into an opening at the underside ofthe piston, from where it gets to the annular cooling duct in theinterior of the piston. During the operation of the engine, the engineoil is thereby supplied with thermal energy which must be dissipated viaappropriate heat exchangers. At full load, the heat to be dissipatedfrom the engine oil is about 4% of the energy supplied with fuel.

Overall, a relatively large amount of oil is required for feeding allfunctional elements appropriately, with the recirculated oil quantity ofan internal combustion engine usually amounting to 0.5 litres/kW fullengine load.

For the generation of oil pressure, oil pumps are usually used in theform of gear pumps which are driven mechanically by the internalcombustion engine via a transmission and therefore are coupled to therotational speed of the internal combustion engine. The delivery rate ofthe gear pumps essentially depends only on the rotational speed so thatappropriate delivery reserves must be provided in order to maintain thenecessary oil pressure in case of low oil viscosity (e.g., at a high oiltemperature) or, respectively, enlarged lubrication gaps. The excessamount of oil has to be branched off via a shutoff valve downstream ofthe oil pump and must be returned to the oil sump. This entails majorenergy losses.

The efforts to render internal combustion engines ever more efficientand economical cause auxiliary drives and system functions such as thelubricating oil and cooling water circuit to be included increasingly inthe overall optimization of internal combustion engines. This isespecially about adapting also the peripheral systems in an optimal andprecise fashion to the motor requirements, avoiding unnecessary losses.

For driving the cooling water and oil pumps for the cooling water and,respectively, oil circuit, powers must be applied which amount toseveral percent of the engine power and therefore cannot be neglectedwhen it comes to further increasing the efficiency of internalcombustion engines.

SHORT DESCRIPTION OF THE INVENTION

It is therefore the object of the present invention to improve theefficiency of an internal combustion engine with respect to the engineoil circuit. In particular, the engine oil supply of the internalcombustion engine is to be optimized in such a way that energy lossesare reduced to an absolute minimum.

This object is achieved by an oil supply system for an internalcombustion engine comprising a lubricating oil circuit in which a firstoil pressure generating device, a first device for oil temperaturecontrol and a second device for oil temperature control are provided,wherein the two devices for oil temperature control are arranged in twoarms of the lubricating oil circuit connected in parallel and whereinthe first oil pressure generating device is arranged in the flowdirection upstream of the branch to the two arms leading to the twodevices for oil temperature control.

In addition, the object is achieved by an internal combustion enginecomprising such an oil supply system.

The two arms of the lubricating oil circuit connected in parallel arerecombined either in the oil sump or still upstream of the oil sump.

Furthermore, a second oil pressure generating device is preferablyprovided which is arranged in the flow direction downstream of the firstdevice for oil temperature control and is arranged in the first arm ofthe first device for oil temperature control.

For example, the second oil pressure generating device may be arrangedupstream of the first device for oil temperature control.

One embodiment is characterized by an oil filter (3) in the flowdirection upstream of the first oil pressure generating device (5).

Preferably, the invention is further characterized by an oil filter inthe first arm of the lubricating oil circuit, preferably downstream ofthe first oil pressure generating device.

Furthermore, the invention may be characterized by an oil filter in thesecond arm of the lubricating oil circuit.

Said oil filter may be arranged upstream of the second device for oiltemperature control.

One embodiment is characterized in that the first oil pressuregenerating device can be driven mechanically by the internal combustionengine via a transmission and is coupled to the rotational speed of theinternal combustion engine, wherein the second oil pressure generatingdevice is driven by a speed-controlled electric motor.

Furthermore, in one embodiment of the invention, a control unit may beprovided by means of which the pressure at the inlet into the oil linesof the lubricating oil circuit can be adapted to the operatingconditions of the internal combustion engine, wherein the rotationalspeed of the second oil pressure generating device is regulated.

Furthermore, it may be provided that, upstream of the first oil pressuregenerating device, an oil filter is arranged in the first arm and in thesecond arm, respectively, each oil filter having a different filterfineness and mesh size, respectively, wherein said filter fineness andmesh size differ from each other by, in each case, at least 100%, basedon the deposited particle diameter.

In addition, it is preferably provided that, with the first oil pressuregenerating device in the operating state, an oil pressure of between 0.6and 1.6 bar can be generated.

Furthermore, it may be provided that, at the second oil pressuregenerating device, the oil pressure at the inlet into the supply linefor the lubrication points and into the cooling oil nozzles of theinternal combustion engine can be regulated depending on the engineload, wherein the pressure at a maximum engine power is by at least 20%higher than at half load.

In a preferred embodiment variant, it is provided that the temperatureof the first device for oil temperature control is adaptable to themotor requirements.

In addition, the invention may be characterized in that the first devicefor oil temperature control comprises a heat exchanger, which maypreferably have a multi-stage design, with both a cooling and a heatingfunction being provided.

In this connection, appropriate control means including control valvesare provided.

It is preferably provided that the oil filter exhibits the smallest meshsize and the highest filter fineness of all oil filters in the firstarm, preferably downstream of the first oil pressure generating device.

In a preferred embodiment variant, it is provided that the second devicefor oil temperature control in the second arm is adjustable to atemperature between 70 and 80° C., preferably to a temperature between70 and 75° C., during the operation of the engine.

The adjustment is thereby independent of the temperature of the engineoil at the inlet into the pressure lines within the internal combustionengine. In this connection, the engine oil in the oil sump of theinternal combustion engine and—if present—in an external oil reservoir,which, however, is incorporated into the engine oil circuit of theinternal combustion engine, is adjusted to an optimum temperature levelby means of a further device for oil temperature control.

Furthermore, it may be provided that, in the second arm, an oil filteris provided the mesh size of which is larger by at least 100% or,respectively, the filter fineness of which is correspondingly lower thanfor the oil filter in the first arm.

In one embodiment variant, it is provided that, viewed in the flowdirection upstream of the first oil pressure generating device, an oilfilter is arranged the mesh size of which is larger by at least 100% or,respectively, the filter fineness of which is lower to this extent thanthat of the oil filter in the second arm.

Furthermore, it may be provided that, starting from the first oilpressure generating device, the oil circuit is branched into two partialcircuits (with the two arms), wherein one partial circuit (first arm)supplies the oil pressure lines of the internal combustion engine withfinely filtered oil, whereas the other partial circuit (second arm) isresponsible for the temperature control of the engine oil in thecrankcase and, if present, in external oil reservoir containers, which,however, are incorporated into the engine oil circuit, and in which anoil filter can be used which causes a separation of dirt particles in arange greater than 20 μm.

One aspect of the invention relates to an internal combustion engine,comprising an oil supply system of the aforementioned type.

The internal combustion engine may be characterized in that the oiltemperature in the pressure line of the internal combustion engine canbe adjusted as a function of the engine load, wherein the oiltemperature at a maximum engine power is by at least 10° C. lower thanat half load.

The internal combustion engine may be characterized in that the firstarm supplies the oil pressure lines of the internal combustion enginewith finely filtered oil, whereas the second arm is responsible for thetemperature control of the engine oil in the crankcase and, if present,in external oil reservoir containers, which, however, are incorporatedinto the engine oil circuit.

Furthermore, the invention relates to a cogeneration plant comprising aninternal combustion engine of the aforementioned type.

The solution to the problem is aimed at a modified configuration of theengine oil circuit, whereby an optimization of the entire assembly ofthe oil supply of the internal combustion engine, including possible oilfilters, is achieved. A special feature of modern high-performanceengines is that they reach very high power densities via a (frequently2-stage) high charging at full load. Ensuring operational reliabilityunder the high mechanical and thermal component loads associatedtherewith requires specially designed and optimized cooling andlubrication systems. Especially for the high load range, for example,large volume flows of engine oil and cooling water must be conveyedthrough the internal combustion engine.

However, increasingly there are applications in which internalcombustion engines are operated predominantly in the medium load rangeand only for a relatively short time at full load or overload, such aswhen consumption peaks must be covered. In contrast to the high loadrange, however, lower oil delivery rates and higher oil temperatures aremore favourable for the medium or low load range.

However, engine oil circuits commonly designed according to the priorart do not make allowances for the different requirements betweenpartial and full load.

The basic concept of the proposed invention forming the subject matteris, however, based precisely on the fact that, depending on the load andthe operating conditions, the oil quantity, the oil supply pressure, theoil temperature and oil filtering can be optimally adapted to therespective requirements.

A central feature of the proposal is that, for oil production andpressure generation, two separate oil pressure generating devices (inparticular oil pumps) connected in series are provided. Furthermore, theoil circuit is separated into two partial circuits, comprising the twoarms, wherein one partial circuit may be provided for supplying thelubrication and cooling points of the internal combustion engine withoil and the other one may be provided for cooling and for the pre- or,respectively, side stream filtration of the engine oil.

FIG. 1 schematically shows the oil circuit of an oil supply system.

The engine oil is sucked from the oil sump (not illustrated) of theinternal combustion engine 1 into the external lubricating oil circuit2. From the internal combustion engine 1, the lubricating oil gets intothe oil filter 3 designed as a pre-filter and, from there, into thefirst oil pressure generating device in the form of an oil pump 4. Atthe oil pump 4, a bypass line with a check valve is provided. Downstreamof the oil pump 4, the lubricating oil circuit 2 is branched into twopartial circuits with two arms 2 a, 2 b. Approximately one third of theengine oil delivered by the first oil pump 4 passes through the firstarm 2 a to the second oil pressure generating device 5 also in the formof an oil pump 5, wherein a bypass line with a check valve 6 isarranged, and, from there, to the device for oil temperature control 7in the form of a preheating or cooling unit 7 and further to the oilfilter 8 in the form of a fine filter. From the oil filter 8, the engineoil gets into the internal combustion engine 1 for supplying thelubrication points and the piston cooling nozzles.

However, the significantly larger part of the circulating engine oilflows through the second arm 2 b in the second partial circuit, whichbranches off between the first and the second oil pumps 4, 5. In thescheme exemplified in FIG. 1, the branching is followed by a switchvalve 9, an oil filter 10, a device for oil temperature control 11 inthe form of a heat exchanger and an oil buffer volume 12, which mayexhibit a bypass 13. Subsequently, the engine oil flows from the arm 2 bback into the oil sump of the internal combustion engine 1. In the oilsump, the two arms 2 a, 2 b reunite.

The purpose of the 2-stage and separate design of the oil pressuregenerating devices 4, 5 is that the oil temperature and the oil pressureand thus the amount of the oil supply into the lubricating oil andcooling oil supply system of the internal combustion engine 1 cantherewith be controlled and regulated independently of the cooling ofthe engine oil as a function of the operating requirements with minimumpump capacities. For this purpose, the second oil pump 5 is driven by aspeed-controlled electric motor which is actuated and controlled,respectively, by the engine management.

The first oil pump 4 conveys the engine oil for the partial circuitswith the two arms 2 a, 2 b and generates a pre-pressure for the secondoil pump 5. In doing so, the first oil pump 4 is unregulated and can bedriven, for example, directly and, respectively, mechanically by theinternal combustion engine 1. Downstream of the second oil pump 5, thefirst device for oil temperature control 7 is arranged in the firstpartial circuit (arm 2 a), which device serves the purpose that, whenthe cold internal combustion engine 1 is started, the oil temperature israised to the ideal temperature for the bearing lubrication (e.g.,50-60° C.), but the oil temperature can be lowered under the coolingwater temperature in the maximum load range. As soon as the internalcombustion engine 1 reaches the nominal speed during the startingoperation, the oil temperature is raised to about 95° C. In the highload range, the oil temperature is again lowered.

Therefore, the first device for oil temperature control 7 is preferablydesigned as a multi-stage and adjustable heat exchanger, which is inheat exchange, for example, with the engine cooling water circuit and/orwith another cooling circuit, for example with a low-temperature coolingcircuit, and/or, as a controllable electrical heating device (e.g., viaan electrical resistance activated by the engine management),constitutes a system component independent of the cooling water circuit.

Downstream of the first device for temperature control 7, the oil filter8 (designed as a fine filter) is arranged which makes sure that noabrasive solid-state particles larger than, for example, 8 μm enter intothe lubricating gaps of the bearing points.

In the second partial circuit (arm 2 b), the cooling of the oil quantityin the oil sump of the internal combustion engine 1 is effected. Forthis purpose, about twice the amount of engine oil which gets into theinternal combustion engine 1 via the arm 2 a is branched off andconducted into the second device for oil temperature control 11 (a heatexchanger). The engine oil of this partial circuit is again conducteddirectly into the oil sump of the internal combustion engine 1, ideallyat the other end of the internal combustion engine 1, from which theengine oil is removed. In this second partial circuit (arm 2 b), furtherfunctional elements may be integrated, for example, a switch valve 9, afurther oil filter 10 and an oil buffer volume 12 (e.g., in the form ofa supplementary oil tank).

The first oil pump 4 produces an oil pressure of between 0.6 and 1.6bar, which basically is sufficient for supplying the internal combustionengine 1 on short notice with lubricating oil in case the second oilpump 5 fails so that enough time remains for a proper shutdown of theinternal combustion engine 1 without any bearing damage or corrosion ofpistons. For this purpose, a bypass line around the second oil pump 5may, for example, be provided, in which a check valve 6 is arranged sothat the pressure downstream of the second oil pump 5 can never fallbelow the pressure downstream of the first oil pump 4. In the event thatthe second oil pump 5 fails, a switch valve 9 is arranged in the secondpartial circuit (arm 2 b) which throttles or blocks the oil flow in saidline correspondingly.

In the second partial circuit (arm 2 b), the main cooling of the engineoil is effected during the operation of the engine. This is done by aheat exchanger 11 which is incorporated into the secondary circuit ofthe engine or, respectively, installation cooling, for example, into thehot-water return flow in applications with power-heat coupling.

The proposed division into two separate partial circuits also has theadvantage that the entire engine oil in the oil sump can thus be broughtto the operating temperature before the start-up of the internalcombustion engine 1. Advantageously, a further oil filter 10 exhibitinga lower filter fineness than filter 8 is integrated into the secondpartial circuit (arm 2 b). Overall, three oil filter 3, 8, 10 aretherefore preferably provided which each have a different filterfineness: oil filter 3 is designed as a coarse filter having arelatively large mesh size (e.g., >50 μm). Oil filter 10 acts as acleaning filter with a mesh size of, e.g., >20 μm, and oil filter 8 actsas a fine filter with a mesh size of approx. 10 μm.

The best results are achieved with the proposed approach if, in additionto the oil temperature, also the oil pressure at the inlet into thelubricating oil supply lines of the internal combustion engine 1 isadapted to the operating requirements of the internal combustion engine1 as precisely as possible.

In the high-load range and in particular in the overload range, asignificantly higher oil pressure is required than under a partial load.According to the invention, the second oil pump 8 is, therefore,operated by the speed-controlled electric motor in such a way that theoptimum oil pressure is always set. This occurs, for example, in thatthe engine management system controls and regulates the drive engineappropriately. The pressure increase is continuously adjustable from 0to 3.5 bar via said second stage. In this way, unnecessary power lossesare avoided, and a safe and efficiency-optimized engine operation isprovided.

Overall, several improvements can thus be achieved simultaneously by theproposed solution as described:

-   -   By dividing the oil production device into two structurally        separate oil pumps, of which the first oil pump 4 provides a        pre-pressure of between 0.6 and 1.6 bar, whereas the second oil        pump 5, which is driven via a speed-controlled electric motor        and is actuated by the engine management, builds up a supply        pressure which is flexibly and optimally adapted to the motor        requirements, a bearing lubrication and a piston cooling which        are optimal for all operating conditions can be ensured with        minimum energy input.    -   By arranging the oil temperature control device 7 between the        second oil pump 5 and the oil filter 8, the oil temperature can        also be adapted optimally to the respective motor requirements,        irrespective of the temperature downstream of the oil cooler. In        this way, a safe and friction-optimized bearing lubrication as        well as a piston cooling situationally adapted in an optimum way        can be achieved under all operating conditions.    -   By dividing the external oil circuit 2 into 2 partial circuits        (arms 2 a and 2 b), the cooling of the stock oil in the        crankcase and (if present) in the supplementary oil tank can be        decoupled from the optimum temperature control of the engine oil        at the inlet into the lubricating oil supply lines and the        cooling nozzles. In this way, said stock oil can be kept at a        temperature as low as possible, whereby thermal oil ageing can        be minimized.    -   By using a total amount of three separate oil filters 3, 8, 10        each having a different mesh size and filter grade,        respectively, in the different partial circuits, namely upstream        of the first oil pump 4, downstream of the oil temperature        control device 7 as well as upstream of the oil cooler, the oil        can be cleaned from abrasive floats and dirt particles in an        efficient manner. The filters used can be optimized specially        for the respective filter grade so that an optimally purified        oil can be obtained therewith with the maximum possible filter        lives.

1-20. (canceled)
 21. An oil supply system for an internal combustionengine, comprising a lubricating oil circuit in which a first oilpressure generating device, a first device for oil temperature control,and a second device for oil temperature control are provided, whereinthe two devices for oil temperature control are arranged in two arms ofthe lubricating oil circuit connected in parallel and wherein the firstoil pressure generating device is arranged in the flow directionupstream of the branch to the two arms leading to the two devices foroil temperature control.
 22. An oil supply system according to claim 21,further comprising a second oil pressure generating device which isarranged in the flow direction downstream of the first device for oiltemperature control and is arranged in the first arm of the first devicefor oil temperature control.
 23. An oil supply system according to claim21, further comprising an oil filter in the flow direction upstream ofthe first oil pressure generating device.
 24. An oil supply systemaccording to claim 21, further comprising an oil filter in the first armof the lubricating oil circuit, wherein the oil filter in the first armof the lubricating oil circuit is downstream of the second oil pressuregenerating device.
 25. An oil supply system according claim 21, furthercomprising an oil filter in the second arm of the lubricating oilcircuit.
 26. An oil supply system according claim 22, wherein the firstoil pressure generating device can be driven mechanically by theinternal combustion engine via a transmission and is coupled to therotational speed of the internal combustion engine, wherein the secondoil pressure generating device is driven by a speed-controlled electricmotor.
 27. An oil supply system according claim 22, further comprising acontrol unit by way of which the pressure at the inlet into the oillines of the lubricating oil circuit can be adapted to the operatingconditions of the internal combustion engine, wherein the rotationalspeed of the second oil pressure generating device is regulated.
 28. Anoil supply system according to claim 23, wherein upstream of the firstoil pressure generating device, an oil filter is arranged in the firstarm and in the second arm, respectively, each oil filter having adifferent filter fineness or mesh size, wherein said mesh sizes differfrom each other by, in each case, at least 100%, based on the mesh sizeof the other oil filter.
 29. An oil supply system according to claim 21,wherein with the first oil pressure generating device is operable togenerate an oil pressure of between 0.6 and 1.6 bar in the operatingstate.
 30. An oil supply system according to claim 22, wherein at thesecond oil pressure generating device, the oil pressure at the inletinto the supply line for the lubrication points and into the cooling oilnozzles of the internal combustion engine can be regulated depending onthe engine load, wherein the pressure at a maximum engine power is by atleast 20% higher than at half load.
 31. An oil supply system accordingto claim 21, wherein the temperature of the first device for oiltemperature control is adaptable to the motor requirements.
 32. An oilsupply system according to claim 21, wherein the temperature of thefirst device for oil temperature control involves a multi-stage heatexchanger, which is incorporated into the cooling circuit for the enginecooling water or into a further cooling circuit and which comprises anelectrical heating device.
 33. An oil supply system according to claim23, wherein the oil filter exhibits the smallest mesh size and thehighest filter fineness of all oil filters in the first arm downstreamof the first oil pressure generating device.
 34. An oil supply systemaccording to claim 21, wherein the second device for oil temperaturecontrol in the second arm is adjustable to a temperature between 70 and80° C. during the operation of the engine.
 35. An oil supply systemaccording to claim 23, wherein in the second arm, an oil filter isprovided the mesh size of which is larger by at least 100% or,respectively, the filter fineness of which is correspondingly lower thanfor the oil filter in the first arm.
 36. An oil supply system accordingto claim 23, wherein viewed in the flow direction upstream of the firstoil pressure generating device, an oil filter is arranged the mesh sizeof which is larger by at least 100% or, respectively, the filterfineness of which is lower to this extent than that of the oil filter inthe second arm.
 37. An internal combustion engine comprising an oilsupply system according to claim
 21. 38. An internal combustion engineaccording to claim 37, wherein the oil temperature in the pressure lineof the internal combustion engine can be adjusted as a function of theengine load, wherein the oil temperature at a maximum engine power is byat least 10° C. lower than at half load.
 39. An internal combustionengine according to claim 37, wherein the first arm supplies the oillines of the internal combustion engine with finely filtered engine oil,whereas the second arm is responsible for the temperature control of theengine oil in the crankcase and, if present, in external oil reservoircontainers, which, however, are incorporated into the engine oilcircuit, as well as for the pre- or, respectively, side streamfiltration of the engine oil.
 40. A cogeneration plant comprising aninternal combustion engine according to claim 39.